This invention relates generally to rotating induction apparatus and more specifically to rotating induction apparatus that are tolerant of harmonics.
In a rotating induction apparatus, a current of electrical charge generated within a magnetic field experiences a force perpendicular to the flow of charge and to the lines of force of the magnetic field. If a conductor is forced through a magnetic field by some sort of an external prime mover, an electrical current is caused to flow; this is the principle of the operation of an electrical generator. When an electrical current flows through a conductor in a magnetic field, a force is applied to the conductor; this is the principle of the operation of an electrical motor.
In an alternating current (AC) induction motor, a rotating magnetic field is produced by the stator or stationary portion of the apparatus. This rotating magnetic field interacts with current carried by conductors of the rotor, causing the rotor to turn. It also produces currents in the rotor conductors by transformer action. Thus, the rotor needs no connections to an electrical supply, and is simply supported by bearings which allow free rotation.
The rotating magnetic field is produced by coils of wire or windings, suitably positioned on the stator. Each winding, when energized with a direct current, would produce a fixed magnetic field. By energizing a winding with a sinusoidal AC, a smooth varying magnetic field of fixed orientation may be produced. By positioning several windings of differing orientations on a single stator and energizing the windings with alternating currents of differing phase, a rotating magnetic field is produced which is the sum of the time-varying fixed orientation magnetic fields generated by each winding/phase. The stator is defined as the stationary part of the magnetic circuit and these stator windings.
The rotating field produced by the stator windings is complex and irregular. By the principal of superposition, the rotating field may be analyzed as being composed of numerous rotating fields of different shape, including a fundamental or desired lowest frequency structure. The rotating field is composed of this fundamental field and higher frequency harmonic fields.
The excitation currents may similarly be complex, and may be analyzed as being composed of several different harmonic currents. The fundamental excitation current is the primary source of torque.
Spatial harmonics, or air-gap harmonics, are harmonic fields generated by the non-sinusoidal nature of the field generated by each winding. When spatial harmonics are excited by the fundamental drive currents, they produce a secondary rotating field that rotates slower than the fundamental field. For a given excitation frequency, spatial harmonic fields rotate more slowly than the fundamental field.
Harmonic fields generated by non-sinusoidal drive wave-forms are termed temporal harmonics. Rotating fields produced by temporal harmonic currents rotate more rapidly than the fundamental field. When temporal harmonics excite the fundamental spatial field, they produce a secondary rotating field that rotates more rapidly than the fundamental field and may rotate in the opposite direction to the fundamental field.
Therefore, both spatial and temporal harmonics in rotating fields may adversely affect the efficiency of a conventional rotating induction apparatus, lowering torque and increasing current flow.
From the foregoing, it may be appreciated that a need has arisen for a rotating induction apparatus that is tolerant of harmonics.
In accordance with an embodiment of the present invention, a rotating induction apparatus comprises: an inverter system that outputs a number of phases, wherein the number is more than three; a stator comprising a plurality of slots and full span concentrated windings, wherein the windings are electrically coupled to the inverter system; a rotor electromagnetically coupled to a magnetic field generated by the stator; and a signal generator generating a drive waveform signal, the drive waveform signal having a fundamental frequency, wherein the drive waveform signal drives the inverter system, and further wherein a pulsing frequency of the drive waveform signal is in fixed phase relation to the fundamental frequency.
In accordance with another embodiment of the present invention, a rotating induction apparatus comprises: an inverter system that outputs two or more phases; a stator comprising a plurality of slots and full span concentrated windings, wherein the windings are electrically coupled to the inverter system; a rotor electromagnetically coupled to a magnetic field generated by the stator; and a signal generator generating a drive waveform signal, wherein the drive waveform signal drives the inverter system and the drive waveform signal is fed to the inverter system through at least one signal delay device.
In accordance with still another embodiment of the present invention, a rotating induction apparatus comprises: an inverter system that outputs more than three phases; a stator comprising a plurality of slots and full span concentrated windings, wherein the windings are electrically coupled to the inverter system; a rotor electromagnetically coupled to a magnetic field generated by the stator; and whereby the inverter system comprises at least one module, wherein the at least one module comprises an inverter.
In accordance with a further embodiment of the present invention, a rotating induction apparatus comprises: an inverter system that outputs at least six phases, wherein the number of phases is a multiple of three; a stator comprising a plurality of slots and full span concentrated windings, wherein the windings are electrically coupled to the inverter system; a rotor electromagnetically coupled to a magnetic field generated by the stator; and whereby the windings are grouped into a plurality of three phase groups, wherein the plurality of three phrase groups is equivalent to the number of phases divided by three.
In accordance with still yet another embodiment of the present invention, a rotating induction apparatus comprises: an inverter system that outputs a number of phases, wherein the number of phases is more than three, the inverter system comprising a number of half bridge inverters equivalent to the number of phases; a stator comprising a plurality of slots and full span concentrated windings, wherein the windings are electrically coupled to the inverter system, wherein half of the windings are driven and the other half of the windings are connected to a star point; a rotor electromagnetically coupled to a magnetic field generated by the stator; and whereby the driven windings are arranged in at least one set of an odd integer number of windings, wherein the odd integer number of windings is the largest odd integer that divides into the number of phases evenly and divides into 360 evenly.
In accordance with still a further embodiment of the present invention, a rotating induction apparatus comprises: an amplifier that generates an alternating current having twelve phases or greater; a stator comprising a plurality of slots and full span concentrated windings, wherein the windings are electrically coupled to the amplifier; and a rotor electromagnetically coupled to a magnetic field generated by the stator.
In accordance with yet a further embodiment of the present invention, a method of operating an electrical rotating apparatus comprises: providing an inverter system that outputs more than three phases; electrically coupling full span concentrated windings of a stator to the inverter system; electromagnetically coupling a rotor to a magnetic field generated by the stator; generating a drive waveform signal from a signal generator; and driving the inverter system with the drive waveform signal, wherein the drive waveform signal has a fundamental frequency, and further wherein a pulsing frequency of the drive waveform signal is in fixed phase relation to the fundamental frequency.
In accordance with another embodiment of the present invention, a method of operating an electrical rotating apparatus comprises: providing an inverter system that outputs three or more phases; electrically coupling full span concentrated windings of a stator to the inverter system; electromagnetically coupling a rotor to a magnetic field generated by the stator; generating a drive waveform signal from a signal generator; feeding the drive waveform signal through at least one signal delay device; and feeding a signal output from the at least one signal delay device to the inverter system.
A technical advantage of the present invention is that it substantially reduces the problems associated with harmonic rotating fields. Another technical advantage of the present invention is that it may employ pulse width modulated signals (PWM). Further, utilizing certain frequencies of the PWM may provide improved apparatus performance.
A further technical advantage is that a single drive waveform signal may be employed to drive all inverters, as opposed to employing multiple, independent drive waveform signals.
Yet another technical advantage is that the present invention facilitates operation in the non-linear region of the saturation curve, or operation at densities greater than about 130,000 lines per square inch (2.02 Tesla). Because the torque varies as the square of the magnetic field strength, operation at high saturation levels substantially increases available torque and motor performance during starting.
Still another technical advantage of the present invention is that it may beneficially use non-sinusoidal drive waveforms produced by slow switching elements. The inverter may also use flexible component sizes, and, therefore, facilitate cheaper per unit capacity power semiconductors.